Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing our new design.

FIG. 2 is a front view of a display screen or portion thereof with a graphical user interface showing our new design in another environment; and,

FIG. 3 is a front view of a display screen or portion thereof with a graphical user interface showing our new design in yet another environment.

The broken lines in the FIGS. showing display screens, portions of display screens, text, and graphical elements form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 